MIMO antenna system

ABSTRACT

A multiple input, multiple output (“MIMO”) antenna system is provided for operation on a radio frequency (“RF”) module that may be used in a wireless access device. The MIMO antenna system includes a plurality of multi-band antenna elements connected to a radio in a MIMO configuration. The multi-band antenna elements and the radio are configured to operate on an RF module. A reflector is formed on the RF module to contain the plurality of multi-band antenna elements and a common director is positioned in front of the multi-band antenna elements to concentrate signal communication in a sector. The plurality of multi-band antenna elements are oriented to provide a sector coverage pattern formed by beam patterns generated by each of the multi-band antenna elements.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims the priority to U.S. Provisional PatentApplication Ser. No. 61/933,783, entitled “Mimo Antenna System,” filedon Jan. 30, 2014, to inventors Abraham Hartenstein, the disclosure ofwhich is incorporated by reference herein in its entirety.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates generally to communication devices and moreparticularly to antennas for Multiple-Input, Multiple-Output (MIMO)media access controllers.

2. Related Art

The use of wireless communication devices for data networking is growingat a rapid pace. Data networks that use “WiFi” (“Wireless Fidelity”),also known as “Wi-Fi,” are relatively easy to install, convenient touse, and supported by the International Electrical and ElectronicEngineers (IEEE) 802.11 standard. WiFi data networks also provideperformance that makes WiFi a suitable alternative to a wired datanetwork for many business and home users.

WiFi networks operate by employing wireless access points that provideusers, having wireless (or “client”) devices in proximity to the accesspoint, with access to varying types of data networks such as, forexample, an Ethernet network or the Internet. The wireless access pointsinclude a radio that operates according to one of three standardsspecified in different sections of the IEEE 802.11 specification.Generally, radios in the access points communicate with client devicesby utilizing omni-directional antennas that allow the radios tocommunicate with client devices in any direction. The access points arethen connected (by hardwired connections) to a data network system thatcompletes the access of the client device to the data network.

The three standards that define the radio configurations are:

-   1. The IEEE 802.11a standard, which operates on the 5 GHz frequency    band with data rates of up to 54 Mbs;-   2. The IEEE 802.11b standard, which operates on the 2.4 GHz    frequency band with data rates of up to 11 Mbs; and-   3. The IEEE 802.11g standard, which operates on the 2.4 GHz    frequency band with data rates of up to 54 Mbs.

The 802.11b and 802.11g standards provide for some degree ofinteroperability. Devices that conform to the 802.11b standard maycommunicate with 802.11g access points. This interoperability comes at acost as access points will switch to the lower data rate of 802.11b ifany 802.11b devices are connected. Devices that conform to the 802.11astandard may not communicate with either 802.11b or 802.11g accesspoints. In addition, while the 802.11a standard provides for higheroverall performance, 802.11a access points have a more limited rangecompared with the range offered by 802.11b or 802.11g access points.

Each standard defines ‘channels’ that wireless devices, or clients, usewhen communicating with an access point. The 802.11b and 802.11gstandards each allow for 14 channels. The 802.11a standard allows for 23channels. The 14 channels provided by the 802.11b and 802.11g standardsinclude only 3 channels that are not overlapping. The 12 channelsprovided by the 802.11a standard are non-overlapping channels.

Access points provide service to a limited number of users. Accesspoints are assigned a channel on which to communicate. Each channelallows a recommended maximum of 64 clients to communicate with theaccess point. In addition, access points must be spaced apartstrategically to reduce the chance of interference, either betweenaccess points tuned to the same channel, or to overlapping channels. Inaddition, channels are shared. Only one user may occupy the channel atany give time. As users are added to a channel, each user must waitlonger for access to the channel thereby degrading throughput.

One way to increase throughput is to employ multiple radios at an accesspoint. Another way is to use multiple input, multiple output (“MIMO”)antennas to communicate with mobile devices in the area of the accesspoint. MIMO has the advantage of increasing the efficiency of thereception. However, MIMO antennas entail using multiple antennas forreception and transmission at each radio. The use of multiple antennasmay create problems with space on the access point, particularly whenthe access point uses multiple radios. In some implementations ofmultiple radio access points, it is desirable to implement a MIMOimplementation in the same space as a previous non-MIMO implementation.

Current MIMO implementations may utilize 2-3 antennas per radio. Whenmore than one antenna is used, the mutual coupling among the antennasdue to their proximity may degrade the performance of the access pointand reduce the throughput. The problem with mutual coupling is magnifiedwhen multiple radios are used in an access point.

It would be desirable to implement MIMO antennas in multiple radioaccess points without significant space constraints such that it wouldbe possible to substitute a non-MIMO multiple radio access point with aMIMO multiple radio access point in the same space. It would also bedesirable to implement MIMO in a multiple radio access point whilemaximizing the performance of the access point in coverage and qualityof service (QOS).

SUMMARY

In view of the above, a multiple input, multiple output (“MIMO”) antennasystem is provided for operation on a radio frequency (“RF”) module thatmay be used in a wireless access device. The MIMO antenna systemincludes a plurality of multi-band antenna elements connected to a radioin a MIMO configuration. The multi-band antenna elements and the radioare configured to operate on a RF module. A reflector is formed on theRF module to contain the plurality of multiband antenna elements and toconcentrate signal communication in a sector, the plurality of multibandantenna elements oriented to provide a sector coverage pattern formed bybeam patterns generated by each of the multi-band antenna elements.

Other systems, methods and features of the invention will be or willbecome apparent to one with skill in the art upon examination of thefollowing figures and detailed description. It is intended that all suchadditional systems, methods, features and advantages be included withinthis description, be within the scope of the invention, and be protectedby the accompanying claims.

BRIEF DESCRIPTION OF THE DRAWINGS

The examples of the invention described below can be better understoodwith reference to the following figures. The components in the figuresare not necessarily to scale, emphasis instead being placed uponillustrating the principles of the invention. In the figures, likereference numerals designate corresponding parts throughout thedifferent views.

FIG. 1 is a perspective view of an example of a radio frequency (“RF”)module that uses a 2-element multi-band multiple input, multiple output(MIMO) antenna array.

FIG. 2A is a schematic diagram illustrating a top view of an example ofan 8-port Wireless Local Area Network (“WLAN”) access device implementedwith an example of the RF module in FIG. 1 that includes a 3-elementmulti-band MIMO antenna array.

FIG. 2B is a schematic diagram illustrating a top view of an example ofa 12-port WLAN access device that uses an example of the RF module shownin FIG. 2A.

FIG. 2C is a schematic diagram illustrating a top view of an example ofa 16-port WLAN access device that uses an example of the RF module shownin FIG. 2A.

FIG. 3 is a schematic diagram of an example implementation of amulti-band antenna element.

FIGS. 4A-4D are schematic diagrams illustrating the use of spatialdiversity to generate a sector coverage pattern using beam patternsgenerated by each of the antenna elements in the 3-element multi-bandMIMO antenna array.

FIG. 4E is a cross-sectional view of the beam patterns shown in FIG. 4Aat broken line E-E′ of FIG. 4A.

FIG. 5 is a block diagram of an example radio that may be used in an RFmodule that includes MIMO-configured multi-band antenna arrays.

FIG. 6 is a perspective view of an example of a RF module that uses a3-element multi-band MIMO antenna array and a reflector.

FIG. 7 is a top view of an example of a RF module that uses a 3-elementmulti-band MIMO antenna array and a reflector as shown in FIG. 6.

FIG. 8 is a schematic diagram illustrating the use of spatial diversityto generate a sector coverage pattern using beam patterns generated byeach of the antenna elements in the 3-element multi-band MIMO antennaarray with a reflector as shown in FIGS. 6 and 7.

FIG. 9 is a schematic diagram of another example implementation of amulti-band antenna element.

FIG. 10 is a schematic diagrams illustrating azimuth coverage in theantenna shown in FIG. 9.

FIG. 11 is a schematic diagrams illustrating elevation coverage in theantenna shown in FIG. 9.

FIG. 12 is a schematic diagram of a switching network for use with theantenna shown in FIG. 9.

DETAILED DESCRIPTION

In the following description of example embodiments, reference is madeto the accompanying drawings that form a part of the description, andwhich show, by way of illustration, specific example embodiments inwhich the invention may be practiced. Other embodiments may be utilizedand structural changes may be made without departing from the scope ofthe invention.

A wireless local area network (“WLAN”) access device that uses a MIMOantenna array is disclosed. The WLAN access device may include acircular housing having a plurality of radial sectors and a plurality ofantenna arrays, each antenna array arranged within individual radialsectors of the plurality of radial sectors.

In general, the antenna arrays used in the WLAN access device includemulti-sector antenna systems that radiate a plurality of radiationpatterns that “carve” up the airspace into equal sections of space orsectors to assure continuous coverage for a client device incommunication with the WLAN antenna array (WLANAA). The radiationpattern overlap may also ease management of a plurality of clientdevices by allowing adjacent sectors to assist each other. For example,adjacent sectors may assist each other in managing the number of clientdevices served with the highest throughput as controlled by an arraycontroller. The WLANAA provides increased directional transmission andreception gain that allow the WLANAA and its respective client devicesto communicate at greater distances than standard omni-directionalantenna systems, thus producing an extended coverage area when comparedto an omni-directional antenna system.

The WLANAA is capable of creating a coverage pattern that resembles atypical omni-directional antenna system but covers approximately fourtimes the area and twice the range. In general, each radio frequency(“RF”) sector is assigned a non-overlapping channel by an ArrayController.

Examples of implementations of a WLANAA in which multiple input,multiple output (“MIMO”) schemes may be implemented, and in whichexample implementations consistent with the present invention may alsobe implemented are described in: PCT Patent Application No.PCT/US2006/008747, filed on Jun. 9, 2006, titled “WIRELESS LAN ANTENNAARRAY,” and incorporated herein by reference in its entirety, and U.S.patent application Ser. No. 12/269,567 filed on Nov. 12, 2008, titled“MIMO Antenna System,” and incorporated herein by reference in itsentirety.

FIG. 1 is a perspective view of an example of an RF module 100 that usesa 2 element multi-band MIMO antenna array. The RF module 100 in FIG. 1includes a printed circuit board (“PCB”) 102, RF processing circuitry104, a first antenna array element 106, a second antenna array element108, a reflector 110, and an edge connector 112 on the PCB 102. The2-element multi-band MIMO antenna array in the RF module 100 in FIG. 1includes two antenna elements 106, 108.

As described below with reference to FIGS. 2A-2C, eight, twelve, orsixteen RF modules 102, respectively, may be connected radially aroundthe controller printed circuit board to create a 365 coverage areaaround the controller. Each RF module 100 is configured to implement aportion of the 365 coverage area. Each portion is substantiallypie-shaped in accordance with the substantially pie shape of the RFmodules 100. The coverage pattern may be configured by the reflector110, the position and layout of the antenna elements 106, 108, and theoperation of the electronic components implemented on the RF module 100.

The reflector 110 is configured to enhance the gain/directivity of theantenna elements 106, 108. The reflector 110 may also be shaped toenhance isolation between adjacent RF modules 100 as well asfront-to-back isolation. For example, as shown in FIG. 1, the reflector110 may be implemented as a three-sided wall that forms two corners onopposite sides of a first side positioned perpendicular to a radial axisthat may extend from a center of a circular configuration of the WLANaccess device. The other two sides of the three-sided wall may formobtuse angles with the first wall to direct radiation in the desiredcoverage pattern. The antenna elements 106, 108 may be positioned in thecorners formed by the three-sided wall of the reflector 110. Thereflector 110 may be made of any suitable material. In oneimplementation, the reflector 110 is made of an aluminum sheet.

The PCB 102 may be any suitable printed circuit board implementation.The PCB 102 shown in FIG. 1 is substantially pie-shaped to fit in acircular configuration with other RF modules 102. The reflector 110 maybe mounted on the PCB 102 with the antenna elements 106, 108 mountedwithin the reflector 110. The antenna elements 106, 108 and thereflector 110 cooperate to radiate a sector coverage pattern outward ina radial direction when mounted in an access device.

The RF processing circuitry 104 may be designed into the PCB 102 toprovide RF signal processing functions. The RF processing circuitry 104may be configured to operate with a controller to implement any suitablewireless LAN system. The RF processing circuitry 104 may communicatewith the controller via the edge connectors 112.

FIGS. 2A-2C illustrate example WLAN access devices implemented using anexample of the RF module 100 in FIG. 1 as an 8-port WLAN access device(FIG. 2A), a 12-port WLAN access device (FIG. 2B), and a 16-port WLANaccess device (FIG. 2C). The example of the RF module 100 that is usedin the implementations illustrated in FIGS. 2A-2C uses 3-elementmulti-band MIMO antenna arrays although a 2-element arrays may be usedas well. The RF modules may all be identical to one another and connectto the controller for configuration and control during implementation.In one example, the controller is configured for each WLAN access devicebased on the number of ports (8, 12, 16).

FIG. 2A is a schematic diagram illustrating a top view of an example ofan 8-port WLAN access device 200 implemented with eight RF modules 202a-h, each of which includes a 3-element antenna array 206 a-c. Each RFmodule 202 a-h also includes a reflector 208, and an edge connector 210,which connects to a mating edge connector 212 on an 8-port WLANcontroller 204. The RF modules 202 a-h in FIG. 2A are configured andarranged to provide coverage patterns in eight sectors. One radiotransceiver in each of the RF modules 202 a-h communicates via thethree-element antenna array 206 a-c connected according to a MIMOscheme. The eight sectors combine to provide a 360 degrees coveragearound the WLAN access device 200.

FIG. 2B is a schematic diagram illustrating a top view of an example ofa 12-port WLAN access device 220 implemented with 12 RF modules 222 a-l.The 12 RF modules 222 a-l each include 3-element antenna arrays similarto the RF modules 202 a-h shown in FIG. 2A. The 12 RF modules 222 a-lare connected to a 12-port WLAN controller 224.

FIG. 2C is a schematic diagram illustrating a top view of an example ofa 16-port WLAN access device 240 implemented with 16 RF modules 242 a-p.The 16 RF modules 242 a-p each include 3-element antenna arrays similarto the RF modules 202 a-h shown in FIG. 2A. The 16 RF modules 242 a-pare connected to a 16-port WLAN controller 244.

FIG. 3 is a schematic diagram of an example implementation of amulti-band antenna element 300 that may be used as a MIMO antenna array.The antenna element 300 in FIG. 3 includes two stacked Vivaldi Notchantennas 302, 304 implemented as a multi-layer board of dielectricsubstrates. The multi-layer board may include traces and patterns ofmetal on different layers of the board. In one example implementation, athree-layer board is used in the antenna element 300 shown in FIG. 3. Inexample implementations, the Vivaldi Notch antenna is a broadbandantenna structure that can cover bandwidth of 10:1 or more.

In a middle layer of the three-layer board, a ‘V’ shaped metallic layermay be formed in the shape of each notch antenna 302, 304 shown in FIG.3. A first ‘V’ shaped metallic element, which forms a top notch antenna302 includes a top curved portion 302 a and a bottom curved portion 302b. A second ‘V’ shaped metallic element, which forms the bottom notchantenna 304 includes a top curved portion 304 a and a bottom curvedportion 302 b. The top and bottom curved portions 302 a, 304 a, and 302b, 304 b, respectively, extend from a center gap 305 and 307 that formsthe ‘V’ shaped pattern. The curved portions 302 a, 302 b, 304 a, 304 bmay be formed in dimensions suitable for receiving and transmittingsignals in the frequency bands needed according to the requirements ofthe WLAN access device. In one example, the antenna elements 302, 304are dimensioned to receive and transmit signals according to the IEEE802.11a/b/g/d/n standards.

The notch antennas 302, 304 in FIG. 3 are configured to operate withinthe space formed by the reflector 106 to provide the desired sectorcoverage pattern. The notch antennas 302, 304 used as corner antennas inthe corners of the reflector 106 are placed at a point in the reflectorcorners that put their phase centers about a quarter wavelength (λ/4)from the corresponding corner. In order for the phase center of theantenna to coincide with that of the corner of the reflector, theantenna needs to shrink in size. As such the 2.4 Ghz band resonatesoutside of the notch zone under the curved portions 302 a, 302 b of theantennas 302. The notch antennas 302, 304 in FIG. 3 may be configured toincrease the gain of the antenna array. The notch antennas 302, 304 forman array that narrows the elevation beam while the azimuth coveragestays the same, which is similar to operation of a single notch antenna.

In order to cover the 2.4 Ghz band, the top curved portion 302 a of thetop notch antenna 302 extends to form a narrowed strip that is curvedwithin the area under the top curved portion 302 a. This first narrowedstrip functions as a top 2.4 Ghz resonating arm 310 a on the top notchantenna 302. The bottom curved portion 302 b of the top notch antenna302 extends to form a narrowed strip that is curved within the areaunder the bottom curved portion 302 b. This second narrowed stripfunctions as a bottom 2.4 Ghz resonating arm 310 b on the top notchantenna 302. The top curved portion 304 a of the bottom notch antenna304 extends to form a narrowed strip that is curved within the areaunder the top curved portion 304 a. This third narrowed strip functionsas a top 2.4 Ghz resonating arm 311 a on the bottom notch antenna 304.The bottom curved portion 304 b of the bottom notch antenna 304 extendsto form a narrowed strip that is curved within the area under the topcurved portion 304 b. This fourth narrowed strip functions as a bottom2.4 Ghz resonating arm 311 b on the bottom notch antenna 304. The fournarrow strips shown in FIG. 3 are coplanar with the top and bottomcurved portions 302 a, 304 a, and 302 b, 304 b, respectively, which maybe in a middle layer of the three-layer board. However, in otherimplementations, portions of the notch antennas 302, 304 including thenarrow strips may be etched on other layers. The narrow strips may alsobe formed in other shapes suitable for capturing signals within thedesired frequency ranges.

The top notch antenna 302 may connect to a top feedline 322 a, which isformed by a metallic trace on another layer, such as on a top layer,which extends to a main feedpoint 318 via common feedline 320 fromcommon feedpoint 324. The top notch antenna 302 may connect to the topfeedline 322 a at a top notch short stub 310, which couples to the topfeedline 322 a via a top notch antenna feedline 312. The shape anddimensions of the top notch short stub 310 and the top notch antennafeedline 312 may be selected in order to provide a proper match with thefeedline all the way to the main feedpoint 318 in the frequency range ofinterest.

The bottom notch antenna 304 may connect to a bottom feedline 322 b,which is formed by a metallic trace on another layer, such as on a toplayer, which extends to a main feedpoint 318 via common feedline 320from common feedpoint 324. The bottom notch antenna 304 may connect tothe bottom feedline 322 b at a bottom notch short stub 314, whichcouples to the bottom feedline 322 b via a bottom notch antenna feedline316. The shape and dimensions of the bottom notch short stub 314 and thebottom notch antenna feedline 316 may be selected in order to provide aproper match with the feedline all the way to the main feedpoint 318 inthe frequency range of interest.

It is noted that the implementation of the multi-band antenna element300 described above is a dual-band antenna for wireless communicationpursuant to 802.11a/n and 802.11b/g/n specifications. The multi-bandantenna element 300 may be configured for implementations based on otherspecifications. In addition, the multi-band antenna element 300 usesVivaldi notch antennas; however, any suitable multi-band antennadesigned may be used. The 2.4 Ghz resonating arms are used to optimizethe coverage of signals around 2.4 Ghz. However, other suitable shapesmay be used as well.

Two or three multi-band antenna elements 300 (in FIG. 3) may be mountedin the RF module 100 (in FIG. 1) and connected to the radio transceiver.In operation, the multi-band antenna elements form coverage patterns,and using spatial diversity provides the desired sector coveragepatterns. The sector coverage patterns may be configured to ensure adesired amount of overlap of coverage as well as a desired amount ofisolation in selected areas. The sector coverage patterns may beconfigured by the orientation of the multi-band antenna element 300within the RF module 100 (FIG. 1), and by controlling operationalfactors that determine the power, sensitivity, range and other factors.Each multi-band antenna element forms a coverage beam, which is combinedwith the other coverage beams to form the sector's coverage pattern. Theoverlap between beams may be controlled along the azimuth by the use ofthe notch antennas. The azimuth coverage of the individual notchantennas is a function of the antenna space formed by the phase centerand the reflector corner.

FIGS. 4A-4D are schematic diagrams illustrating the use of spatialdiversity to generate a sector coverage pattern using beam patternsgenerated by each of the antenna elements in the 3-element multi-bandMIMO antenna array.

FIG. 4A illustrates a spatial diversity 400 obtained from thecombination of the beam patterns from each antenna element. The spatialdiversity 400 in FIG. 4A is generated by an RF module 402 having threemulti-band antenna elements 404 a-c, and a reflector 406. The threemulti-band antenna elements 404 a-c may be implemented as describedabove with reference to FIG. 3. Any suitable multi-band antenna elementmay be used instead. FIG. 4A depicts a 3-element multi-band antennaarray formed by the three multi-band antenna elements 404 a-c.

The RF module 402 generates three beams 410 a-c using the threemulti-band antenna elements 404 a-c, each antenna element 404 a-cgenerating a corresponding beam 410 a-c. FIG. 4B depicts a first beam410 a generated by the first of the three antenna elements 404 apositioned in the lower-left hand corner of the reflector 406. The firstbeam 410 a radiates along a first center axis 412 a extending from thefirst antenna element 404 a. As shown in FIG. 4C, a center beam 410 b isformed by a center one of the three antenna elements 404 b. The centerbeam 410 b radiates along a second center axis 412 b extending from thecenter antenna element 404 b. As shown in FIG. 4D, a third beam 410 c isgenerated by a third of the three antenna elements 404 c. The third beam410 c radiates along a third center axis 412 c extending from the centerantenna element 404 c. The three resulting beam 410 a-c are arrange in aspatial diversity setting where the beams cover different sections ofthe sector with a desired degree of overlap.

The beams 410 a-c generated by each antenna element 404 a-c are formedby the directivity provided by the antenna elements 404 a-c and by shapeand geometry of the reflector 406. The reflector 406 is shaped in orderto provide the isolation required for the different sectors to operateat full capacity without interfering with the other sectors. Thereflector 406 also enhances the antenna gain in the desired frequencybands. The reflector 406 has two corner reflector portions as describedabove with reference to FIG. 1. One of the 3-multi-band antenna elementsis mounted in each of the two corner reflector portions, shown as 404 aand 404 c (referring to FIG. 4A). Each of the corner antennas 404 a,c isplaced at a point in the corner that puts its phase center about aquarter wavelength (λ/4) from the corner. The third (center) antenna 404b is placed in the center of the reflector 406 and generates the centerbeam 410 b.

The corner antennas 404 a,c, which form beams 410 a,b relative to thereflector corners are positioned to generate the two beams 410 a,c suchthat they overlap and are squinted from a boresight. FIG. 4E is across-sectional view of the beam patterns shown in FIG. 4A at E-E′illustrating a view of the beam patterns from a position facing theantenna arrays into the physical boresight of the antenna array 404. Itis noted that the view in FIG. 4E assumes that the view in FIG. 4A isfrom under the RF module 400 and that the RF module 400 is installedabove the users, such as on a ceiling. The view in FIG. 4E shows thefirst beam 410 a generated by the first antenna element 404 a, thecenter beam 410 b generated by the center antenna element 404 b, and thethird beam 410 c generated by the third antenna element 404 c. The firstbeam 410 a and the third beam 410 c are shown squinted from theboresight. In an example implementation, the first and third beams 410a,c may be squinted by about +/−35° degree., although the squinting maybe any suitable angle range. A two-element antenna array may be usedresulting in the coverage pattern defined by the two overlapping cornerbeams 410 a,b modified by configuring and orienting the antenna elements404 a,c to generate beams that adequately cover the sector. In the3-element antenna array, the center antenna is included to generatethree overlapping beams 410 a-c providing the sector coverage patternshown in FIGS. 4A and 4E. The three overlapping beams enable MIMOoperation with low correlation between the two or three channels coupledto the radio receiver.

FIG. 5 is a block diagram of an example radio that may be used in an RFmodule that includes MIMO configured multi-band antenna arrays. FIG. 5depicts a MIMO channel circuit 500 that may be implemented in an RFmodule 100 (in FIG. 1). Multiple MIMO channel circuits 500 may be usedin a MIMO configured RF sector implemented with the RF module 100 (inFIG. 1). Two channel circuits 500 may be configured for a 2×2 MIMOimplementation. Three channel circuits 500 may be configured for a 3×3or a 2×3 MIMO implementation.

The MIMO channel circuit 500 in FIG. 5 includes a transceiver 502, a 5Ghz receiver/transmitter pair 504 a and 504 b, a 2 Ghzreceiver/transmitter pair 505 a and 505 b, a front-end module (“FEM”)506, band selector switch 508, a diplexer 510, a high-band line 512, alow-band line 514, and a dual-band antenna 520. The MIMO channel circuit500 shown in FIG. 5 may be configured for operation as a 2 Ghz receiverand/or transmitter, or a 5 Ghz receiver and/or transmitter according to802.11a/n or 802.11g/b/n.

The transceiver 502 may be any suitable radio transceiver configured foroperation according to 802.11a/b/g/n standards. The transceiver 502 maybe switched to operate according to one of the standards and to operateas a receiver, a transmitter, or both. Based on the switch and selectedstandard, the transceiver 502 enables either the 2 Ghz receiver and/ortransmitter lines 504 a,b or the 5 Ghz receiver and/or transmitter lines505 a,b.

The dual-band antenna 502 may include any suitable multi-band antenna,including for example, a Vivaldi notch antenna array such as themulti-band antenna array described above with reference to FIG. 3. Thedual-band antenna 502 is connected to the diplexer 510. The diplexer 510receives a signal having combined high (5 Ghz) and low (2 Ghz) signals,separates the signals and couples each to corresponding high and lowconnections 512, 514, which switch between high frequency and lowfrequency signals. In the example shown in FIG. 5, the high (5 Ghz)signal is coupled to the high connection 512, and the low signal (2 Ghz)is coupled to the low connection 514.

The high connection 512 and the low connection 514 are connected to theband selector switch 508, which may be switched to determine whichsignal to receive and/or transmit and to enhance the isolation betweenthe two frequency modes. The band selector switch 508 is configured suchthat the un-selected connection is coupled to a resistor connected toground. The resistor is provided with a high resistance to provide ahigh impedance connection for the unselected signal.

The selected signal path (i.e., high or low connection) is coupled tothe FEM 506. The FEM 506 conditions the signal by using poweramplifiers, low noise amplifiers, and filters for the desired signaltypes. In one example, the FEM 506 may be implemented using a SE595LDual Band 802.11n Wireless LAN Front End made by SIGe Semiconductors.

The FEM 506 is connected to the 2 Ghz receiver and/or transmitter lines504 a,b or the 5 Ghz receiver and/or transmitter lines 505 a,b toreceive 2 Ghz or 5 Ghz signals from the wireless transceiver 502 overeither the 2 Ghz or 5 Ghz transmitter lines 504 a, 505 a; or to couple 2Ghz or 5 Ghz signals to the wireless transceiver 502 over either the 2Ghz or 5 Ghz receiver lines 504 b, 505 b.

In general, the present invention disclosed includes the development ofantenna architecture for a MIMO WiFi access point. The antenna isdesigned to enhance the performance of the access point in coverage andquality of service (QOS). Current MIMO technology requires 2-3 antennasper radio, compared with one antenna per radio in the early days. As thenumber of antenna increase, the mutual coupling among the antennas dueto their proximity might degrade the performance of the access point andreduce the throughput. The problem becomes more important in cases wheremultiple radios are used. As a system level solution, 802.11a/b/g/n—theantenna solution for the access point is modular. As can be seen in FIG.1, the RF module assembly is a standalone card which is designed tointerface with the mother board/controller in the center of the accesspoint. The RF module includes the RF front end, the antenna PCBs,reflector and interfaces. The RF module can be used in any of the 8, 12or 16 port access points (see FIG. 2A). The antennas in the RF modulecould serve the 2×2, 2×3 or 3×3 MIMO schemes. In those cases, the numberof the antennas per module will be 2 or 3. Each of the antennas is adual band where the antenna is a two stacked notched array (see FIG. 3).The antennas are placed in front of a reflector that is designed for twopurposes: 1) the reflector is shaped in order to provide the isolationrequired for the different sectors to operate in full capacity withoutinterfering with the other sectors (see FIG. 4A); and 2) the reflectoris designed to enhance the antenna gain in both bands. The reflector ascan be seen in FIGS. 1 and 4, has two corner reflectors as part of itsdesign. Each of the corner antennas is placed at a point that its phasecenter is about a quarter wavelength (λ/4) from the corner. The thirdantenna is placed in the center of the reflector and fills up the centerof the sector (beam 3 410 b). The position of the corner antennas (beams1 410 a and 2 410 c) relative to the reflector corners is critical ingenerating two overlapping beams and squinted from boresight by about+/−35° (see FIG. 4). When the third antenna is included, threeoverlapping beams are created covering the sector. This effect iscritical to the MIMO operation where the two or three channels leadingto the receiver are with low correlation.

As far as an example of antenna solutions in an 802.11a/b/g/n antenna,the antennas in each of the RF modules may be dual band ones(802.11a/b/g/n). The basic antenna element as can be seen in FIG. 3 is aVivaldi Notch antenna. The Vivaldi Notch antenna is a broadband antennastructure that can cover bandwidth of 10:1 or more. The Vivaldi Notchantenna is widely used in military and space applications. The VivaldiNotch antenna in this application may be a dual band antenna structure.In order for the phase center of the antenna to coincide with that ofthe corner reflector, the antenna needs to shrink in size. As such the2.4 Ghz band is resonating outside of the notch zone (see 2.4 Ghzresonating arm in FIG. 3), in the two extensions of the arms. In orderto achieve more directivity, each of the antennas may be made from anarray of two stacked Vivaldi Notch antennas (see FIG. 3). The array PCBassembly is a multi-layered PCB assembly containing the Notch antennasand their beam forming network (BFN).

In general, the antenna solution is modular where the radio and itsantennas are considered to be a module. Each module includes a reflectorto enhance gain/directivity of the antennas. The reflectors have a shapeto enhance the isolation between the modules. Each module is assigned toa specific sector. Each of the antennas is a dual band one (802.11a/nand 802.11b/g/n). Each module can have 2 or 3 antennas. The threeresulting beam are arrange in a space diversity setting where the two orthree beams cover different sections of the sector with a certainoverlap. The reflectors are high enough to provide a good front/back(F/B) performance which is critical to isolation performance to sectorsat 180 degrees directions. Each of the antennas is a two element arrayof stacked Vivaldi Notch antennas. Each antenna assembly is amulti-layer design of dielectric substrates.

Another example building on the original antenna discussed above (inrelation to FIGS. 1-5) is the antenna 600 shown in FIG. 6, FIG. 7, andFIG. 8. Like the original antenna, the antenna 600 includes threeantenna elements 610, 620, 630 in front of a shaped reflector 640, allof which are mounted on an RF card 660. Each antenna element 610, 620,630 is a dual band antenna element. The directivity of the originalantenna depends on reflector size as a function of wavelength. At the802.11b/g/n frequency band (2.4 Ghz), the antenna directivity is lowerthan that in the 802.11a/n frequency band (5 Ghz). By adding a director650 in the right position, relative to the three antenna elements, onecan enhance the directivity.

In general, the director 650 is positioned in an optimal point relativeto the three antenna elements 610, 620, 630; as an example, the director650 may be spaced about a quarter wavelength (λ/4) from the antennaelements. The Yagi effect is usually narrow band and as such, thedirector 650 needs to be frequency dependent to enhance the 802.11b/g/nmode and not affect the 802.11a/n mode. The director can be optimized inmany ways to enhance one or two bands per system requirements. Thedirector 650 may be optimized by breaking it into sections coupled toeach other forming a frequency selective director. The director 650 ispassive and is not connected to any circuitry or ground on the RF card660.

In general, a director may be added to the RF card 660 in the properposition relative to the three antenna elements 610, 620, 630 in orderto create a Yagi effect. The proper position may be a fractionalwavelength of the operating frequency. Unlike the standard Yagi antennawhere the director(s) are dedicated to one antenna, in the antenna 600,one director 650 is common to all three antenna elements. The director650 is multi sectional in order to have its performance frequencydependent. The director 650 is designed to enhance the directivity ofthe antennas at the 802.11b/g/n mode, and not affect the directivity atthe 802.a/n mode. The director can be realized in several forms such astubular, printed PCB, etc. The antenna elements 610, 620, 630, inconjunction with the reflector 640 and director 650, form respectivebeams 615, 625, 635.

Also described in this application is an omnidirectional antenna to beused in WLAN MIMO outdoor applications. The antenna coverage can becontrolled depending on the specific installation. In WLAN employingWiFi MIMO technology for outdoor use, there is a need to have severalomni antennas within the same radome. The architecture of such a systembecomes quite involved as more than one MIMO radio is involved (2×2 or3×3). An important feature is the ability to achieve multiple radiooperating in coexistence sharing the same spectral range. As such, theomnidirectional antenna system is made from subarrays as shown in FIG.9. Each subarray is made from one, two broadband or dual band antennaelements. The antenna elements could be a dualband dipole or a VivaldiNotch. The two antenna elements of the subarray may be spaced such thatthe array factors in either of the operating bands will not suffer fromhigh sidelobe levels. The antenna system may be fabricated usingstandard PCB etching of a PCB microwave grade material. Each subarraymay be a standalone and is connected via a coaxial cable interface asshown in FIG. 9.

In the antenna system in FIG. 10 two subarrays are facing on directionwhile the other two are facing the opposite direction. If more channelsor MIMO radios will be used, the number of subarrays will increaseaccordingly. The subarrays facing opposite directions have cardiodazimuth coverage which yield very sharp nulls (see FIG. 10) that resultin high isolation between the two subarrays group (>40 dB). Thesubarrays facing the same direction are separated along the E-plane ofthe antenna element which typically have null along the zenith direction(see FIG. 11). This fact help achieve high isolation (>40 dB) betweenthe subarrays. When subarrays 1 and 3 are connected to one radio (2×2)and subarrays 2 and 4 are connected to second radio (2×2) an omni modeis achieved with high isolation between the radios (>40 dB) enabling theWiFi radios to operate with no interference. When subarrays 1 and 2 areconnected to one radio (2×2) and subarrays 3 and 4 are connected to thesecond WiFi MIMO radio (2×2) a sectored mode is achieved. Each radiowill cover a sector close to 180 in azimuth (see FIG. 11). In thesectored mode the two radios achieve high isolation (>40 dB) whichenable them to operate with no interference. By adding a switchingnetwork (see FIG. 12), the omni and sectored modes could be selected onthe fly.

It will be understood that the foregoing description of numerousimplementations has been presented for purposes of illustration anddescription. It is not exhaustive and does not limit the claimedinventions to the precise forms disclosed. For example, the aboveexamples have been described as implemented according to IEEE 802.11aand 802.11bg. Other implementations may use other standards. Inaddition, examples of the wireless access points described above may usehousings of different shapes, not just round housing. The number ofradios in the sectors and the number of sectors defined for any givenimplementation may also be different. Modifications and variations arepossible in light of the above description or may be acquired frompracticing the invention.

It will be understood that various aspects or details of the inventionmay be changed without departing from the scope of the invention. It isnot exhaustive and does not limit the claimed inventions to the preciseform disclosed. Furthermore, the foregoing description is for thepurpose of illustration only, and not for the purpose of limitation.Modifications and variations are possible in light of the abovedescription or may be acquired from practicing the invention. The claimsand their equivalents define the scope of the invention.

What is claimed is:
 1. A multiple input, multiple output (“MIMO”)antenna system comprising: a plurality of multi-band antenna elementsconnected to a radio in a multiple MIMO configuration, the multi-bandantenna elements and the radio operating on a radio frequency (“RF”)module; a reflector formed to contain the plurality of multi-bandantenna elements and to concentrate signal communication in a sector,the plurality of multi-band antenna elements oriented to provide asector coverage pattern formed by beam patterns generated by each of themulti-band antenna elements; and a director, common to all of theplurality of multi-band antenna elements, disposed between the pluralityof multi-band antenna elements and the sector.
 2. The MIMO antennasystem of claim 1 where: the reflector includes a three-sided wall thatforms two corners on opposite sides of a first side positionedperpendicular to a radial axis extending from an opposite end of the RFmodule, the three-sided wall having an opening opposite the first side.3. The MIMO antenna system of claim 1 where: each of the plurality ofmultiband antenna elements includes at least one notch antenna printedon a printed circuit board where the multi-band antenna element ismounted perpendicular to the RF module with a ‘V’ pattern formed by thenotch antenna open towards the sector.
 4. The MIMO antenna system ofclaim 2 where: the plurality of multi-band antenna elements includes afirst multi-band antenna element mounted in a first of the two cornersand a second multi-band antenna element mounted in a second of the twocorners formed by the reflector, the first and second multi-band antennaelements including a notch antenna printed on a printed circuit boardwhere the multi-band antenna element is mounted perpendicular to the RFmodule along the corners of the reflector with a ‘V’ pattern formed bythe notch antenna open towards the sector, the first and secondmulti-band antenna element being oriented to generate crossing beampatterns.
 5. The MIMO antenna system of claim 4 where: the plurality ofmulti-band antenna elements further includes a third multi-band antennaelement including a notch antenna printed on a printed circuit boardwhere the multiband antenna element is mounted perpendicular to the RFmodule substantially midway between the corners of the reflector the ‘V’pattern formed by the notch antenna open towards the sector, the thirdmulti-band antenna element being oriented to generate a beam patternalong a physical boresight of the sector.
 6. The MIMO antenna system ofclaim 5 where the first and second multi-band antenna elements areoriented to squint relative to the physical boresight of the sector. 7.The MIMO antenna system of claim 4 where the first and second multi-bandantenna elements are positioned in the reflector corners at a pointapproximately a quarter wavelength (λ/4) from the corresponding corner.8. The MIMO antenna system of claim 3 where each of the multi-bandantenna elements includes a pair of notch antennas arranged to directthe ‘V’ pattern formed by the notch antennas in the same direction, thenotch antennas arranged as a stack when the multiband antenna elementsare mounted perpendicular to the RF module.
 9. The MIMO antenna systemof claim 3 where each notch antenna includes a resonating arm extendingfrom each portion that forms the ‘V’ pattern.
 10. A wireless local areanetwork (“WLAN”) radio frequency (“RF”) module comprising: a printedcircuit board having RF processing circuitry; a plurality of multi-bandantenna elements connected to the RF processing circuitry in a multipleinput, multiple output (“MIMO”) configuration; a reflector formed tocontain the plurality of multi-band antenna elements and to concentratesignal communication in a sector, the plurality of multi-band antennaelements oriented to provide a sector coverage pattern formed by beampatterns generated by each of the multi-band antenna elements; and adirector, common to all of the plurality of multi-band antenna elements,disposed between the plurality of multi-band antenna elements and thesector.
 11. The WLAN RF module of claim 10 where the reflector includesa three-sided wall that forms two corners on opposite sides of a firstside positioned perpendicular to a radial axis extending from anopposite end of the RF module, the three-sided wall having an openingopposite the first side.
 12. The WLAN RF module of claim 10 where: eachof the plurality of multi-band antenna elements includes at least onenotch antenna printed on a printed circuit board where the multi-bandantenna element is mounted perpendicular to the RF module with a ‘V’pattern formed by the notch antenna open towards the sector.
 13. TheWLAN RF module of claim 11 where: the plurality of multi-band antennaelements includes a first multi-band antenna element mounted in a firstof the two corners and a second multi-band antenna element mounted in asecond of the two corners formed by the reflector, the first and secondmulti-band antenna elements including a notch antenna printed on aprinted circuit board where the multi-band antenna element is mountedperpendicular to the RF module along the corners of the reflector with a‘V’ pattern formed by the notch antenna open towards the sector, thefirst and second multi-band antenna element being oriented to generatecrossing beam patterns.
 14. The WLAN RF module of claim 13 where: theplurality of multi-band antenna elements further includes a thirdmulti-band antenna element including a notch antenna printed on aprinted circuit board where the multiband antenna element is mountedperpendicular to the RF module substantially midway between the cornersof the reflector the ‘V’ pattern formed by the notch antenna opentowards the sector, the third multi-band antenna element being orientedto generate a beam pattern along a physical boresight of the sector. 15.The WLAN RF module of claim 14 where the first and second multi-bandantenna elements are oriented to squint relative to the physicalboresight of the sector.
 16. The WLAN RF module of claim 13 where thefirst and second multi-band antenna elements are positioned in thereflector corners at a point approximately a quarter wavelength (λ/4)from the corresponding corner.
 17. The WLAN RF module of claim 12 whereeach of the multi-band antenna elements includes a pair of notchantennas arranged to direct the ‘V’ pattern formed by the notch antennasin the same direction, the notch antennas arranged as a stack when themultiband antenna elements are mounted perpendicular to the RF module.18. The WLAN RF module of claim 12 where each notch antenna includes aresonating arm extending from each portion that forms the ‘V’ pattern.19. The WLAN RF module of claim 10 where the WLAN RF module isconfigurable to communicate in accordance with either the 802.11an orthe 802.11bgn standards, the WLAN RF module further comprising: adiplexer connected to each multi-band antenna element and to a highfrequency line and a low frequency line; and a front end moduleconnected to either the high frequency line or the low frequency line,the front end module configured: to connect the high frequency line andthe low frequency line to a high transmit line corresponding the highfrequency line and a low transmit line corresponding to the lowfrequency line for radio signals being communicated from the radio tothe multi-band antenna element, and to connect the high frequency lineand the low frequency line to a high receive line corresponding the highfrequency line and a low receive line corresponding to the low frequencyline for radio signals being communicated to the radio from themulti-band antenna element.
 20. A wireless LAN access device comprising:a plurality of RF modules radially connected to a central controller toprovide a 365-degree coverage pattern divided into sectors of coveragepattern provided by corresponding RF modules, each RF module including:a printed circuit board having RF processing circuitry; a plurality ofmulti-band antenna elements connected to the RF processing circuitry ina MIMO configuration; a reflector formed to contain the plurality ofmulti-band antenna elements and to concentrate signal communication in asector, the plurality of multi-band antenna elements oriented to providea sector coverage pattern formed by beam patterns generated by each ofthe multi-band antenna elements; and a director, common to all of theplurality of multi-band antenna elements, disposed between the pluralityof multi-band antenna elements and the sector.
 21. The wireless LANaccess device of claim 20 where the reflector on each RF module includesa three-sided wall that forms two corners on opposite sides of a firstside positioned perpendicular to a radial axis extending from anopposite end of the RF module, the three-sided wall having an openingopposite the first side.
 22. The wireless LAN access device of claim 20where: each of the plurality of multi-band antenna elements on each RFmodule includes at least one notch antenna printed on a printed circuitboard where the multi-band antenna element is mounted perpendicular tothe RF module with a ‘V’ pattern formed by the notch antenna opentowards the sector.
 23. The wireless LAN access device of claim 21where: the plurality of multiband antenna elements on each RF moduleincludes a first multi-band antenna element mounted in a first of thetwo corners and a second multi-band antenna element mounted in a secondof the two corners formed by the reflector, the first and secondmulti-band antenna elements including a notch antenna printed on aprinted circuit board where the multi-band antenna element is mountedperpendicular to the RF module along the corners of the reflector with a‘V’ pattern formed by the notch antenna open towards the sector, thefirst and second multi-band antenna element being oriented to generatecrossing beam patterns.
 24. The wireless LAN access device of claim 23where: the plurality of multi-band antenna element on each RF modulefurther includes a third multi-band antenna element including a notchantenna printed on a printed circuit board where the multi-band antennaelement is mounted perpendicular to the RF module substantially midwaybetween the corners of the reflector the ‘V’ pattern formed by the notchantenna open towards the sector, the third multi-band antenna elementbeing oriented to generate a beam pattern along a physical boresight ofthe sector.
 25. The wireless LAN access device of claim 24 where thefirst and second multiband antenna elements on each RF module areoriented to squint relative to the physical boresight of the sector. 26.The wireless LAN access device of claim 23 where the first and secondmultiband antenna elements on each RF module are positioned in thereflector corners at a point approximately a quarter wavelength (λ/4)from the corresponding corner.
 27. The wireless LAN access device ofclaim 22 where each of the multi-band antenna elements on each RF moduleincludes a pair of notch antennas arranged to direct the ‘V’ patternformed by the notch antennas in the same direction, the notch antennasarranged as a stack when the multi-band antenna elements are mountedperpendicular to the RF module.
 28. The wireless LAN access device ofclaim 22 where each notch antenna includes a resonating arm extendingfrom each portion that forms the ‘V’ pattern.
 29. The wireless LANaccess device of claim 20 where each RF module is configurable tocommunicate in accordance with either the 802.11an or the 802.11bgnstandards, the RF module further comprising: a diplexer connected toeach multi-band antenna element and to a high frequency line and a lowfrequency line; a front end module connected to either the highfrequency line or the low frequency line, the front end moduleconfigured: to connect the high frequency line and the low frequencyline to a high transmit line corresponding the high frequency line and alow transmit line corresponding to the low frequency line for radiosignals being communicated from the radio to the multi-band antennaelement, and to connect the high frequency line and the low frequencyline to a high receive line corresponding the high frequency line and alow receive line corresponding to the low frequency line for radiosignals being communicated to the radio from the multi-band antennaelement.